In pressure measurement technology, absolute—and relative-pressure sensors are used, for example. In the case of absolute-pressure sensors, a pressure to be measured is registered in absolute terms, i.e. as a pressure difference with respect to a vacuum. With a relative-pressure sensor, a pressure to be measured is picked up in the form of a pressure difference with respect to a reference pressure, for example a pressure which prevails where the sensor is located. In most applications, this is the atmospheric pressure at the place of use. Consequently, in the case of the absolute-pressure sensor a pressure to be measured is sensed in relation to a fixed reference pressure, the vacuum pressure, and in the case of the relative-pressure sensor a pressure to be measured is registered in relation to a variable reference pressure, for example ambient pressure.
Ceramic pressure-measuring cells are advantageously used in pressure measurement technology, since ceramic pressure-measuring cells have a measuring accuracy which is stable over a very long time. One reason for this is the solid ionic bonding of ceramic, which makes the material very durable and undergo virtually no ageing in comparison with other materials, for example metals. However, in comparison with metal, ceramic pressure sensors have a rougher surface and are often restrained by means of a generally nonreplaceble seal made of an organic material, for example an elastomer, in a pressure-tight manner in a housing which can then fastened at a measuring location by means of a process connection.
In the food industry, pressure sensors which can be fitted such that they are flush at the front are used with preference, all sensor elements coming into contact with a medium of which the pressure is to be measured consisting of a metal, preferably of a stainless steel which can be cleaned very well.
In this branch of industry it is additionally of particular advantage if the pressure sensors have as few seals as possible. Seals consist of organic materials and, for reasons of hygiene, should therefore preferably be replaceable. In an ideal case, there is just a single seal for sealing off the process connection. In contrast to a seal belonging to the sensor, this seal, referred to hereafter as the process seal, can be exchanged at any time by the user himself without any problem, in particular without any effect on the measuring accuracy of the pressure sensor.